Cotransplantation of HLA-identical sibling culture-expanded mesenchymal stem cells and hematopoietic stem cells in hematologic malignancy patients

Toll-like receptors 3 and 4 are expressed by human bone marrow-derived mesenchymal stem cells and can inhibit their T-cell modulatory activity by impairing Notch signaling

Bone marrow (BM)-derived mesenchymal stem cells (MSCs) are multipotent, nonhemopoietic progenitors that also possess regulatory activity on immune effector cells through different mechanisms. We demonstrate that human BM-derived MSCs expressed high levels of Toll-like receptors (TLRs) 3 and 4, which are both functional, as shown by the ability of their ligands to induce nuclear factor kappaB (NF-kappaB) activity, as well as the production of interleukin (IL)-6, IL-8, and CXCL10. Of note, ligation of TLR3 and TLR4 on MSCs also inhibited the ability of these cells to suppress the proliferation of T cells, without influencing their immunophenotype or differentiation potential. The TLR triggering effects appeared to be related to the impairment of MSC signaling to Notch receptors in T cells. Indeed, MSCs expressed the Notch ligand Jagged-1, and TLR3 or TLR4 ligation resulted in its strong downregulation. Moreover, anti-Jagged-1 neutralizing antibody and N[N-(3,5-difluorophenacetyl-l-alanyl)]-S-phenylglycine t-butyl ester (DAPT), an inhibitor of Notch signaling, hampered the suppressive activity of MSCs on T-cell proliferation. These data suggest that TLR3 and TLR4 expression on MSCs may provide an effective mechanism to block the immunosuppressive activity of MSCs and therefore to restore an efficient T-cell response in the course of dangerous infections, such as those sustained by double-stranded RNA viruses or Gram-negative bacteria, respectively.

Mesenchymal stem cells inhibit natural killer-cell proliferation, cytotoxicity, and cytokine production: role of indoleamine 2,3-dioxygenase and prostaglandin E2

Recently, a number of clinical trials used either mesenchymal stem cells (MSCs) or natural killer (NK) cells in an attempt to improve the effectiveness of hematopoietic stem cell transplantation (HSCT). In view of the relevant role of both MSCs and NK cells in HSCT, we have recently explored the result of possible interactions between the 2 cell types. We found that activated NK cells could kill MSCs, whereas MSCs strongly inhibited interleukin-2 (IL-2)-induced NK-cell proliferation. In this study, we further analyzed the inhibitory effect exerted by MSCs on NK cells. We show that MSCs not only inhibit the cytokine-induced proliferation of freshly isolated NK cells but also prevent the induction of effector functions, such as cytotoxic activity and cytokine production. Moreover, we show that this inhibitory effect is related to a sharp down-regulation of the surface expression of the activating NK receptors NKp30, NKp44, and NKG2D. Finally, we demonstrate that indoleamine 2,3-dioxygenase and prostaglandin E2 represent key mediators of the MSC-induced inhibition of NK cells.

Use of stem cells for the treatment of multiple sclerosis

The reported evidence of neurodegeneration in multiple sclerosis (MS) may explain the lack of efficacy of the currently used immunomodulating modalities and the irreversible axonal damage, which results in accumulating disability. To date, efforts for neuroprotective treatments have not been successful in clinical studies in other CNS diseases. Therefore, for MS, the use of stem cells may provide a logical solution, since these cells can migrate locally into the areas of white-matter lesions (plaques) and have the potential to support local neurogenesis and rebuilding of the affected myelin. This is achieved both by support of the resident CNS stem cell repertoire and by differentiation of the transplanted cells into neurons and myelin-producing cells (oligodendrocytes). Stem cells were also shown to possess immunomodulating properties, inducing systemic and local suppression of the myelin-targeting autoimmune lymphocytes. Several types of stem cells (embryonic and adult) have been described and extensively studied in animal models of CNS diseases and the various models of MS (experimental autoimmune encephalomyelitis [EAE]). In this review, we summarize the experience with the use of different types of stem cells in CNS disease models, focusing on the models of EAE and describe the advantages and disadvantages of each stem cell type for future clinical applications in MS.

Multipotent mesenchymal stromal cells and immune tolerance

Multipotent mesenchymal stromal cells or mesenchymal stem cells (MSC) are isolated mainly from bone marrow and adipose tissue but are identified in other tissues such as synovium, periosteum or placenta. They are characterised by their property to adhere to plastic, their phenotype and their ability to differentiate into three lineages (chondrocytes, osteoblasts and adipocytes). More recently, these cells were shown to escape immune recognition and inhibit immune responses. MSC may modulate the function of the major immune cell populations, including antigen-presenting cells, T cells, B cells and natural killer cells. The aim of this review is to focus on the molecular mechanisms, still poorly understood, which are responsible of the immunosuppressive effects mediated by the MSC. Finally, the data obtained from in vivo experimentation in various animal models as well as potential therapeutic applications will be presented.

Therapeutic applications of mesenchymal stromal cells

Mesenchymal stromal cells (MSC) are multipotent cells that can be derived from many different organs and tissues. They have been demonstrated to play a role in tissue repair and regeneration in both preclinical and clinical studies. They also have remarkable immunosuppressive properties. We describe their application in settings that include the cardiovascular, central nervous, gastrointestinal, renal, orthopaedic and haematopoietic systems. Manufacturing of MSC for clinical trials is also discussed. Since tissue matching between MSC donor and recipient does not appear to be required, MSC may be the first cell type able to be used as an "off-the-shelf" therapeutic product.

Adult human fibroblasts are potent immunoregulatory cells and functionally equivalent to mesenchymal stem cells

Bone marrow mesenchymal stem cells (MSC) have potent immunosuppressive properties and have been advocated for therapeutic use in humans. The nature of their suppressive capacity is poorly understood but is said to be a primitive stem cell function. Demonstration that adult stromal cells such as fibroblasts (Fb) can modulate T cells would have important implications for immunoregulation and cellular therapy. In this report, we show that dermal Fb inhibit allogeneic T cell activation by autologously derived cutaneous APCs and other stimulators. Fb mediate suppression through soluble factors, but this is critically dependent on IFN-gamma from activated T cells. IFN-gamma induces IDO in Fb, and accelerated tryptophan metabolism is at least partly responsible for suppression of T cell proliferation. T cell suppression is reversible, and transient exposure to Fb during activation reprograms T cells, increasing IL-4 and IL-10 secretion upon restimulation. Increased Th2 polarization by stromal cells is associated with amelioration of pathological changes in a human model of graft-vs-host disease. Dermal Fb are highly clonogenic in vitro, suggesting that Fb-mediated immunosuppression is not due to outgrowth of rare MSC, although dermal Fb remain difficult to distinguish from MSC by phenotype or transdifferentiation capacity. These results suggest that immunosuppression is a general property of stromal cells and that dermal Fb may provide an alternative and accessible source of cellular therapy.

Application of multipotent mesenchymal stromal cells in pediatric patients following allogeneic stem cell transplantation

Multipotent mesenchymal stromal cells (MSC) have immunomodulatory effects. The aim of this study was to demonstrate safety and feasibility of MSC transfusion in pediatric patients who had undergone allogeneic stem cell transplantation from MMFD, MUD, MMUD and MSD. Patients with posttransplant complications based on deregulated immune effector cells who may benefit from an immunomodulatory effect of MSC had been selected. MSC were isolated from the hematopoietic stem cell donors in five cases and from a third party parental donor in two cases. We transfused ex vivo-expanded MSC in 11 doses into seven pediatric patients. Cell doses were escalated based on availability from 0.4x10(6) to 3.0x10(6) per kg bodyweight No adverse effects were detected with a maximum follow-up of 29 months. One out of three patients showed slight improvement of chronic GVHD. Two patients with severe acute GvHD did not progress to cGvHD. One patient received MSC to stabilize graft function after secondary haploidentical transplantation. One patient recovered from trilineage failure due to severe hemophagocytosis. This is the first case of a pediatric patient treated with MSC for trilineage failure after haploidentical stem cell transplantation from her father. We report the first series of 11 transfusions of expanded MSC in pediatric patients with immunological complications after allogeneic transplantation. Transfusion of MSC was safe and encouraging improvements in some patients were observed.

Human platelet lysate can replace fetal bovine serum for clinical-scale expansion of functional mesenchymal stromal cells

BACKGROUND

Human multipotent mesenchymal stromal cells (MSCs) are promising candidates for a growing spectrum of regenerative and immunomodulatory cellular therapies. Translation of auspicious experimental results into clinical applications has been limited by the dependence of MSC propagation from fetal bovine serum (FBS).

STUDY DESIGN AND METHODS

The capacity of human platelet lysate (HPL) to replace FBS for clinical-scale MSC propagation was analyzed.

RESULTS

HPL could be efficiently produced from buffy coats. Multiplex analyses allowed a distinct HPL growth factor profile to be delineated. With a previously established two-step clinical-scale procedure, HPL was reproducibly more efficient than FBS in supporting MSC outgrowth. With only 3 x 10(5) primary culture-derived MSCs, a mean of 4.36 x 10(8) HPL-MSCs (range, 3.01 x 10(8)-5.40 x 10(8)) was obtained within a single secondary 11- to 13-day culture step. Although morphologically distinct, HPL-MSCs and FBS-MSCs did not differ significantly in terms of immunophenotype, differentiation potential in vitro, and lack of tumorigenicity in nude mice in vivo.

CONCLUSIONS

Replacing FBS with HPL prevents bovine prion, viral, and zoonose contamination of the stem cell product. This new efficient FBS-free two-step procedure for clinical-scale MSC propagation may represent a major step toward challenging new stem cell therapies.

Immunosuppressive effects of mesenchymal stem cells: involvement of HLA-G

INTRODUCTION

Mesenchymal stem cells (MSCs) possess unique immunomodulatory properties. They are able to suppress allogenic T-cell response and modify maturation of antigen-presenting cells. Their role in the treatment of severe graft versus host disease has been reported. The underlying molecular mechanisms of immunosuppression are currently being investigated. Histocompatibility locus antigen (HLA)-G is a nonclassical major histocompatibility complex class I antigen with strong immune-inhibitory properties.

METHODS

We studied the role of HLA-G on MSC-induced immunosuppression. The expression of HLA-G on human MSCs cultured alone and in mixed lymphocytes reaction (MSC/MLR) was analyzed.

RESULTS

We found that HLA-G can be detected on MSCs by real-time reverse-phase polymerase chain reaction, immunofluorescence, flow cytometry (52.4+/-3.6%), and enzyme-linked immunosorbent assay in the supernatant (38.7+/-5.2 ng/mL). HLA-G protein expression is constitutive and the level is not modified upon stimulation by allogenic lymphocytes in MSC/MLR. The functional role of HLA-G protein expressed by MSCs was analyzed using the 87G anti-HLA-G blocking antibody in a MSC/MLR. We found that blocking HLA-G molecule significantly raised lymphocyte proliferation in MSC/MLR (35.5%, P=0.01).

CONCLUSION

Our findings provide evidences supporting involvement of HLA-G in the immunosuppressive properties of MSCs. These results emphasize the potential application of MSCs as a relevant therapeutic candidate in transplantation.

Human platelet lysate allows expansion and clinical grade production of mesenchymal stromal cells from small samples of bone marrow aspirates or marrow filter washouts

We compared two protocols for the expansion of human mesenchymal stromal cells (hMSCs) starting from diagnostic samples of BM aspirates (2-5 ml) or using the remnants in the bag and filter at the end of the BM infusions. The protocols differed in the presence of either 10% fetal bovine serum (FBS) or 5% platelet lysate (PL). We obtained a significantly (P=0.02) better expansion with PL, obtaining a median 1010-fold compared to 198-fold with a selected batch of FBS and in fewer days (29.8 in PL versus 41.4 in FBS). Overall, we recovered a variable number from 54.8 x 10(6) to 365 x 10(6) hMSCs in PL versus a variable number from 2.7 x 10(6) to 31 x 10(6) in FBS. No difference could be found in terms of gross morphology, differentiation potential, surface markers and immunological properties (inhibition of allogeneic PHA response and mixed lymphocyte reaction) of cells expanded with PL or FBS. The preparations were found within the range of acceptability for all the quality control criteria. Due to the clinical grade nature of the PL and the reproducibility of separate preparations, we propose this method to obtain hMSCs even from minute amounts of BM cells.

Two steps to functional mesenchymal stromal cells for clinical application

BACKGROUND

Ex vivo expansion of multipotent mesenchymal stromal cells (MSCs) is a prerequisite for evaluating their therapeutic potential in ongoing clinical trials. Even large volumes of starting material and extended culture periods, however, do not necessarily produce 2 x 10(6) MSCs per kg per adult patient. A new two-step procedure has been devised to propagate more than 1 x 10(8) MSCs from small marrow volumes within fewer than 4 weeks.

STUDY DESIGN AND METHODS

The influence of log fold decreased MSC seeding (2500, 250, 25, 2.5/cm(2)) on clinical-scale expansion, MSC phenotype, and immunomodulatory function combined with multiplex cytokine display was analyzed. Maintenance of MSC characteristics was tested in fibroblast colony-forming unit and differentiation assays.

RESULTS

Reduced seeding density boosted MSC propagation. Low-density expanded MSCs were CD29+, CD73+, CD90+, CD105+, CD14-, CD34-, CD45-, HLA-DR-; retained their differentiation potential; and inhibited lymphocyte proliferation. This was accompanied by deregulated cytokine production. Seeding 0.7 x 10(6) to 1 x 10(6) MSCs derived from a 10- to 13-day primary culture at a low density of 28 to 40 per cm(2) permitted propagation of 1.5 x 10(8) to 3.7 x 10(8) functional MSCs within a 13- to 15-day secondary expansion step.

CONCLUSION

Primary seeding of only 10-mL marrow aspirates on approximately 0.2-m(2) culture area (Step 1) followed by expansion on 2.5 m(2) (Step 2) is sufficient to consistently generate at least 1.5 x 10(8) MSCs in fetal bovine serum-supplemented medium within less than 4 weeks. The efficiency of this two-step procedure for clinical-scale MSC propagation may facilitate rational clinical testing of MSC-based therapies.

Immunomodulatory properties of mesenchymal stromal cells

Mesenchymal stem cells (MSCs) are multipotential nonhematopoietic progenitor cells capable of differentiating into multiple lineages of the mesenchyme. MSCs have emerged as a promising therapeutic modality for tissue regeneration and repair. Further clinical interest has been raised by the observation that MSCs are immunoprivileged and, more importantly, display immunomodulatory capacities. Although the mechanisms underlying the immunosuppressive effects of MSCs have not been clearly defined, their immunosuppressive properties have already been exploited in the clinical setting. The aim of this review is to critically discuss the immunogenicity and immunomodulatory properties of MSCs, both in vitro and in vivo, the possible underlying mechanisms, the potential clinical use of MSCs as modulators of immune responses in vivo, and to indicate clinical safety concerns and recommendations for future research.

Concise review: mesenchymal stem cells: their phenotype, differentiation capacity, immunological features, and potential for homing

MSCs are nonhematopoietic stromal cells that are capable of differentiating into, and contribute to the regeneration of, mesenchymal tissues such as bone, cartilage, muscle, ligament, tendon, and adipose. MSCs are rare in bone marrow, representing approximately 1 in 10,000 nucleated cells. Although not immortal, they have the ability to expand manyfold in culture while retaining their growth and multilineage potential. MSCs are identified by the expression of many molecules including CD105 (SH2) and CD73 (SH3/4) and are negative for the hematopoietic markers CD34, CD45, and CD14. The properties of MSCs make these cells potentially ideal candidates for tissue engineering. It has been shown that MSCs, when transplanted systemically, are able to migrate to sites of injury in animals, suggesting that MSCs possess migratory capacity. However, the mechanisms underlying the migration of these cells remain unclear. Chemokine receptors and their ligands and adhesion molecules play an important role in tissue-specific homing of leukocytes and have also been implicated in trafficking of hematopoietic precursors into and through tissue. Several studies have reported the functional expression of various chemokine receptors and adhesion molecules on human MSCs. Harnessing the migratory potential of MSCs by modulating their chemokine-chemokine receptor interactions may be a powerful way to increase their ability to correct inherited disorders of mesenchymal tissues or facilitate tissue repair in vivo. The current review describes what is known about MSCs and their capacity to home to tissues together with the associated molecular mechanisms involving chemokine receptors and adhesion molecules.

Regulation of MHC Class II Expression and Antigen Processing in Murine and Human Mesenchymal Stromal Cells by IFN-γ, TGF-β, and Cell Density

Mesenchymal stromal cells (MSC) possess immunosuppressive properties, yet when treated with IFN-gamma they acquire APC functions. To gain insight into MSC immune plasticity, we explored signaling pathways induced by IFN-gamma required for MHC class II (MHC II)-dependent Ag presentation. IFN-gamma-induced MHC II expression in mouse MSC was enhanced by high cell density or serum deprivation and suppressed by TGF-beta. This process was regulated by the activity of the type IV CIITA promoter independently of STAT1 activation and the induction of the IFN regulatory factor 1-dependent B7H1/PD-L1 encoding gene. The absence of direct correlation with the cell cycle suggested that cellular connectivity modulates IFN-gamma responsiveness for MHC II expression in mouse MSC. TGF-beta signaling in mouse MSC involved ALK5 and ALK1 TGF-beta RI, leading to the phosphorylation of Smad2/Smad3 and Smad1/Smad5/Smad8. An opposite effect was observed in human MSC where IFN-gamma-induced MHC II expression occurred at the highest levels in low-density cultures; however, TGF-beta reduced IFN-gamma-induced MHC II expression and its signaling was similar as in mouse MSC. This suggests that the IFN-gamma-induced APC features of MSC can be modulated by TGF-beta, serum factors, and cell density in vitro, although not in the same way in mouse and human MSC, via their convergent effects on CIITA expression.

Cotransplantation of ex vivo expanded mesenchymal stem cells accelerates lymphocyte recovery and may reduce the risk of graft failure in haploidentical hematopoietic stem-cell transplantation

Haploidentical hematopoietic stem-cell transplantation (HSCT) is associated with an increased risk of graft failure. Adult bone marrow-derived mesenchymal stromal cells (MSCs) have been shown to support in vivo normal hematopoiesis and to display potent immune suppressive effects. We cotransplanted donor MSCs in 14 children undergoing transplantation of HLA-disparate CD34(+) cells from a relative. While we observed a graft failure rate of 15% in 47 historic controls, all patients given MSCs showed sustained hematopoietic engraftment without any adverse reaction. In particular, children given MSCs did not experience more infections compared with controls. These data suggest that MSCs, possibly thanks to their potent immunosuppressive effect on alloreactive host T lymphocytes escaping the preparative regimen, reduce the risk of graft failure in haploidentical HSC transplant recipients.

Mesenchymal stem cells of cord blood origin are effective at preventing but not treating graft-versus-host disease

The immunosuppressive properties of mesenchymal stem cells (MSC) make them particularly attractive to manipulate graft-versus-host disease (GVHD). So far, the experience of using MSC to treat GVHD is limited to a few cases, controversial results come from preclinical models and several issues remain to be clarified. The present studies were designed to address these questions in a xenogenic model testing the ability of umbilical cord blood-derived MSC (UCB-MSC) to prevent and/or treat GVHD. Sublethally irradiatiated non-obese diabetic/severe combined immunodeficiency NOD/SCID mice transplanted with human peripheral blood mononuclear cells (huPBMC) showed extensive human T-cell proliferation in the peripheral blood, lymphoid and non-lymphoid tissues, which evolved in extensive GVHD (wasting, ruffled hair and hunched back). The mice treated with a single dose of UCB-MSC did not behave differently form the controls. However, when UCB-MSC were given at weekly intervals, there was a marked decrease in human T-cell proliferation and none of the mice developed GVHD. No therapeutic effect was obtained if UCB-MSC were administered at onset of GVHD. This work supports the clinical use of MSC in stem cell transplantation as a prophylaxis rather than treatment of GVHD.

Humanized system to propagate cord blood-derived multipotent mesenchymal stromal cells for clinical application

Background: Umbilical cord blood (UCB) is an easily accessible alternative source for multipotent mesenchymal stromal cells (MSCs) and is generally believed to provide MSCs with a higher proliferative potential compared with adult bone marrow. Limitations in cell number and strict dependence of expansion procedures from selected lots of fetal bovine serum have hampered the progress of clinical applications with UCB-derived MSCs. Methods: We analyzed the isolation and proliferative potential of human UCB MSCs compared with bone marrow MSCs under optimized ex vivo culture conditions. We further investigated human platelet lysate as an alternative to replace fetal bovine serum for clinical-scale MSC expansion. Clonogenicity was determined in colony-forming units-fibroblast assays. MSC functions were tested in hematopoiesis support, vascular-like network formation and immune modulation potency assays. Results: MSCs could be propagated from UCB with and without fetal bovine serum. MSC propagation was effective in 46% of UCB samples. Once established, the proliferation kinetics of UCB MSCs did not differ significantly from that of bone marrow MSCs under optimized culture conditions, resulting in more than 50 population doublings after 15 weeks. A clinical quantity of 100 million MSCs with retained differentiation potential could be obtained from UCB MSCs within approximately 7 weeks. Ex vivo expansion of hematopoietic UCB-derived CD34+ cells as well as immune inhibition and vascular-like network formation could be shown for UCB MSCs propagated under both culture conditions. Conclusion: We demonstrate for the first time that human MSCs can be obtained and propagated to a clinical quantity from UCB in a completely bovine serum-free system. Surprisingly, our data argue against a generally superior proliferative potential of UCB MSCs. Functional data indicate the applicability of clinical-grade UCB MSCs propagated with human platelet lysate-conditioned medium for hematopoiesis support, immune regulation and vascular regeneration.

Towards in situ tissue repair: human mesenchymal stem cells express chemokine receptors CXCR1, CXCR2 and CCR2, and migrate upon stimulation with CXCL8 but not CCL2

The recruitment of bone marrow CD34- mesenchymal stem- and progenitor cells (MSC) and their subsequent differentiation into distinct tissues is the precondition for in situ tissue engineering. The objective of this study was to determine the entire chemokine receptor expression profile of human MSC and to investigate their chemotactic response to the selected chemokines CCL2, CXCL8 and CXCL12. Human MSC were isolated from iliac crest bone marrow aspirates and showed a homogeneous population presenting a typical MSC-related cell surface antigen profile (CD14-, CD34-, CD44+, CD45-, CD166+, SH-2+). The expression profile of all 18 chemokine receptors was determined by real-time PCR and immunohistochemistry. Both methods consistently demonstrated that MSC express CC, CXC, C and CX(3)C receptors. Gene expression and immunohistochemical analysis documented that MSC express chemokine receptors CCR2, CCR8, CXCR1, CXCR2 and CXCR3. A dose-dependent chemotactic activity of CXCR4 and CXCR1/CXCR2 ligands CXCL12 and CXCL8 (interleukin-8) was demonstrated using a 96-well chemotaxis assay. In contrast, the CCR2 ligand CCL2 (monocyte chemoattractant protein-1, MCP-1) did not recruited human MSC. In conclusion, we report that the chemokine receptor expression profile of human MSC is much broader than known before. Furthermore, for the first time, we demonstrate that human MSC migrate upon stimulation with CXCL8 but not CCL2. In combination with already known data on MSC recruitment and differentiation these are promising results towards in situ regenerative medicine approaches based on guiding of MSC to sites of degenerated tissues.

Management of acute graft-versus-host disease

Acute graft-versus-host disease (GvHD) is a frequent complication of allogeneic haemopoietic stem cell transplantation (HSCT) and donor lymphocyte infusions (DLI). Its incidence and severity depends on several factors, such as prophylaxis method, donor/recipient matching, intensity of the conditioning regimen and composition of the graft. Significant progress has been made in recent years in understanding the pathogenesis of the disease, and some of these advances have been translated into clinical trials. First-line treatment of acute GvHD is based on corticosteroids, and produce sustained responses in 50-80% of patients depending on the initial severity. Non-responders are offered second-line therapy, with combinations of immunosuppressive agents, but 1-year survival is 30% in most large trials. New strategies explored include infusion of expanded mesenchymal stem cells (MSC), down regulation of antigen-presenting cells (APC) and suicide gene transduced T cells. Acute GvHD is complicated by severe immunodeficiency causing life-threatening infections. To date, GvHD has not been differentiated from the graft-versus-leukaemia effect. The present review will discuss some of these aspects.

Transplantation of mesenchymal stem cells to enhance engraftment of hematopoietic stem cells

Seven patients underwent treatment with mesenchymal stem cells (MSCs), together with allogeneic hematopoietic stem cell transplantation (HSCT). MSCs were given to three patients for graft failure and four patients were included in a pilot study. HSCT donors were three human leukocyte antigen (HLA)-identical siblings, three unrelated donors and one cord blood unit. The conditioning was myeloablative in four patients and reduced in three patients. MSC donors were HLA-identical siblings in three cases and haploidentical in four cases. Neutrophil counts >0.5 x 10(9)/l was reached at a median of 12 (range 10-28) days. Platelet counts >30 x 10(9)/l was achieved at a median of 12 (8-36) days. Acute graft-versus-host disease (GVHD) grade 0-I was seen in five patients. Two patients developed grade II, which in one patient evolved into chronic GVHD. One severe combined immunodeficiency (SCID) patient died of aspergillosis, the others are alive and well. One patient, diagnosed with aplastic anemia had graft failure after her first transplantation and severe Henoch-Schönlein Purpura (HSP). After retransplantation of MSCs and HSCs, she recovered from both the HSP and aplasia. Thus, co-transplantation of MSC resulted in fast engraftment of absolute neutrophil count (ANC) and platelets and 100% donor chimerism, even in three patients regrafted for graft failure/rejection.

[The hopes of the mesenchymal stem cells in regenerative medicine]

The mesenchymal stem cells are a cell population of bone marrow, which have the capacity to differentiate towards all the cells from the locomotor apparatus. They also have immunomodulatory properties and can contribute to tissue repair, thanks to the secretion of many growth factors. Such cells are also found in the cord blood. In the same way, very close stem cells exist in great quantity in fat tissue. These cells are very good candidates in regenerative medicine. Besides, several clinical trials were carried out in order to highlight their effectiveness mainly in osseous repair and also during hematopoietic stem cells graft or cardiac repair after infarction. However, these trials will be able to develop fully only with the condition that culture techniques meeting the conditions of good manufacturing practice are set-up. This presentation gives a progress report on the whole of these subjects.

Optimization of in vitro expansion of human multipotent mesenchymal stromal cells for cell-therapy approaches: further insights in the search for a fetal calf serum substitute

There is great interest in mesenchymal stromal cells (MSCs) for cell-therapy and tissue engineering approaches. MSCs are currently expanded in vitro in the presence of fetal calf serum (FCS); however, FCS raises concerns when used in clinical grade preparations. The aim of this study was to evaluate whether MSCs expanded in medium supplemented with platelet-lysate (PL), already shown to promote MSC growth, are endowed with biological properties appropriate for cell-therapy approaches. We confirm previously published data showing that MSCs expanded in either FCS or PL display comparable morphology, phenotype, and differentiation capacity, while PL-MSCs were superior in terms of clonogenic efficiency and proliferative capacity. We further extended these data by investigating the immune-regulatory effect of MSCs on the alloantigen-specific immune response in mixed lymphocyte culture (MLC). We found that MSCs-PL are comparable to MSCs-FCS in their capacity to: (i) decrease alloantigen-induced cytotoxic activity; (ii) favor differentiation of CD4+ T-cell subsets expressing a Treg phenotype; (iii) increase early secretion of IL-10 in MLC supernatant, as well as induce a striking augmentation of IL-6 production. As compared with MSCs-PL, MSCs-FCS were more efficient in suppressing alloantigen-induced lymphocyte subset proliferation and reducing early IFNgamma-secretion. Resistance to spontaneous transformation into tumor cells of expanded MSCs was demonstrated by molecular karyotyping and maintenance of normal morphology/phenotype after prolonged in vitro culture. Our data support the immunological functional plasticity of MSCs and suggest that MSCs-PL can be used as an alternative to MSCs-FCS, although these latter cells might be more suitable for preventing/treating alloreactivity-related immune complications.

From the laboratory bench to the patient's bedside: an update on clinical trials with mesenchymal stem cells

Mesenchymal Stem Cells (MSCs) are non-hematopoietic multi-potent stem-like cells that are capable of differentiating into both mesenchymal and non-mesenchymal lineages. In fact, in addition to bone, cartilage, fat, and myoblasts, it has been demonstrated that MSCs are capable of differentiating into neurons and astrocytes in vitro and in vivo. MSCs are of interest because they are isolated from a small aspirate of bone marrow and can be easily expanded in vitro. As such, these cells are currently being tested for their potential use in cell and gene therapy for a number of human diseases. Nevertheless, there are still some open questions about origin, multipotentiality, and anatomical localization of MSCs. In this review, we discuss clinical trials based on the use of MSCs in cardiovascular diseases, such as treatment of acute myocardial infarction, endstage ischemic heart disease, or prevention of vascular restenosis through stem cell-mediated injury repair. We analyze data from clinical trials for treatment of osteogenesis imperfecta (OI), which is a genetic disease characterized by production of defective type I collagen. We describe progress for neurological disease treatment with MSC transplants. We discuss data on amyotrophic lateral sclerosis (ALS) and on lysosomal storage diseases (Hurler syndrome and metachromatic leukodystrophy). A section of review is dedicated to ongoing clinical trials, involving MSCs in treatment of steroid refractory Graft Versus Host Disease (GVHD); periodontitis, which is a chronic disease affecting periodontium and causing destruction of attachment apparatus, heart failure, and bone fractures. Finally, we will provide information about biotech companies developing MSC therapy.

Mesenchymal stem cells: a new strategy for immunosuppression?

In vitro-generated mesenchymal stem cells (MSCs) initially attracted interest for their ability to undergo differentiation toward cells of different lineages. More recently, a major breakthrough was the discovery that MSCs exert a profound inhibitory effect on T cell proliferation in vitro and in vivo. Subsequently, MSCs were shown also to exert similar effects on B cells, dendritic cells and natural killer cells. These results suggested that MSCs could be used to dampen immune-mediated diseases and transplant rejection. It is possible that some of the beneficial effects of MSCs might reflect, in part, the trophic and protective activities they exert on injured cells and tissues, rather than resulting from a true transdifferentiation. In immune-mediated diseases, the protective effects might function in concert with the immunosuppressive and anti-inflammatory activities.

Cotransplantation of cord blood hematopoietic stem cells and culture-expanded and GM-CSF-/SCF-transfected mesenchymal stem cells in SCID mice

Mesenchymal stem cells (MSC) are multipotent in nature and believed to facilitate the engraftment of hematopoietic stem cells (HSC) when transplanted simultaneously in animal studies and even in human trials. In this study, we transfected culture-expanded MSC with granulocyte macrophage-colony stimulating factor (GMCSF) and stem cell factor (SCF) cytokine genes and then cotransplanted with mononuclear cells (MNC) to further promote HSC engraftment. MNC were harvested from cord blood and seeded in long-term culture for ex vivo MSC expansion. A total of 1 x 10(7) MNC plus MSC/microL were introduced to the tail vein of nonobese diabetic/severe combined immunodeficiency mice. After 6-8 weeks later, homing and engraftment of human cells were determined by flow cytometry and fluorescence in situ hybridization studies. The total nucleated cell count and the engraftment of CD45+/CD34+ cells and XX or XY positive human cells were significantly increased in cotransplanted mice and even higher with the cytokine gene-transfected MSC (GM-CSF>SCF, p<0.05) than in transplantation of MNC alone. These results suggest that MSC transfected with hematopoietic growth factor genes are capable of enhancing the hematopoietic engraftment. Delivering genes involved in homing and cell adhesions, CXCR4 or VLA, would further increase the efficiency of stem cell transplantation in the future.

IL-10-transduced bone marrow mesenchymal stem cells can attenuate the severity of acute graft-versus-host disease after experimental allogeneic stem cell transplantation

Recent data suggest that adult mesenchymal stem cells (MSCs) might enhance allogeneic hematopoietic engraftment and prevent graft-versus-host disease (GVHD) owing to their immunosuppressive nature. Using a murine model of acute GVHD, this study examined whether or not the immunosuppressive properties of MSCs could reduce the severity of experimental GVHD. The early injection of MSCs after transplant did not attenuate the severity of acute GVHD. Therefore, this study investigated whether or not the use of IL-10-transduced MSCs (IL-10 MSCs) could reduce the severity of acute GVHD. Lethally irradiated recipients were transplanted and injected with IL-10 MSCs, the MSC-expressing vector alone (vector MSCs), or the diluent (controls), respectively, on day +1. Compared with the vector MSCs or controls, there was a significantly lower mortality in the recipients of the IL-10 MSCs at day 50 after the transplant (percent survival, 0 or 10 vs 70%, P=0.0004 or 0.0064, respectively). The decrease in mortality was confirmed by the semi-quantitative GVHD score (P<0.05), and was associated with decreased serum levels of the pro-inflammatory cytokines, IFN-gamma, on day +7 (P=0.015). Therefore, beneficial effects on GVHD were observed when MSCs were engineered to express the anti-inflammatory cytokine, IL-10.

Impairment in immuno-modulatory function of Flk1(+)CD31(-)CD34(-) MSCs from MDS-RA patients

OBJECTIVE

Myelodysplastic syndromes are a group of hematopoietic disorders characterized by hematopoietic stem cell dysregulation and abnormalities in the immune system. Mesenchymal stem cells (MSCs) and their derived stromal cells constitute a bone marrow microenvironment, which is the niche for hematopoiesis and a key compartment for immune development and regulation. Existing evidence has shown that MSCs from MDS patients have impaired capacity in supporting hematopoiesis. Here, we conducted an investigation to determine whether the immuno-modulatory function of MSCs is also impaired in MDS-RA (refractory anemia) patients.

METHOD

Flk1(+)CD31(-)CD34(-) MSCs were isolated from 15 MDS-RA patients and cultured for testing biological and immunological characteristics.

RESULTS

MDS-RA patient-derived Flk1(+)CD31(-)CD34(-) MSCs showed normal morphology, phenotype and karyotype but appeared impaired in immuno-modulatory function. The capacity of patient Flk1(+)CD31(-)CD34(-) MSCs to inhibit T lymphocyte activation and proliferation was impaired in vitro. In conclusion, MDS-RA patient-derived MSCs have impaired immuno-modulatory functions, suggesting that the dysregulation of hematopoiesis and immune response may originate from MSCs rather than HSCs. MSCs might be a potential target for developing efficacious cures for MDS.

Advances in the understanding of acute graft-versus-host disease

Allogeneic stem cell transplantation (SCT) remains the definitive immunotherapy for malignancy. However, morbidity and mortality due to graft-vs.-host disease (GVHD) remains the major barrier to its advancement. Emerging experimental data highlights the immuno-modulatory roles of diverse cell populations in GVHD, including regulatory T cells, natural killer (NK) cells, NK T cells, gammadelta T cells, and antigen presenting cells (APC). Knowledge of the pathophysiology of GVHD has driven the investigation of new rational strategies to both prevent severe GVHD and treat steroid-refractory GVHD. Novel cytokine inhibitors, immune-suppressant agents known to preserve or even promote regulatory T-cell function and the depletion of specific alloreactive T-cell sub-populations all promise significant advances in the near future. As our knowledge and therapeutic options expand, the ability to limit GVHD whilst preserving anti-microbial and tumour responses becomes a realistic prospect.

Mesenchymal stem cells facilitate the induction of mixed hematopoietic chimerism and islet allograft tolerance without GVHD in the rat

Induction of hematopoietic chimerism and subsequent donor-specific immune tolerance via bone marrow transplantation is an ideal approach for islet transplantation to treat type-1 diabetes. We examined the potential of mesenchymal stem cells (MSCs) in the induction of chimerism and islet allograft tolerance without the incidence of graft-versus-host disease (GVHD). Streptozotocin-diabetic rats received a conditioning regimen consisting of antilymphocyte serum and 5 Gy total body irradiation, followed by an intraportal co-infusion of allogeneic MSCs, bone marrow cells (BMCs) and islets. Although all the recipients rejected the islets initially, half of them developed stable mixed chimerism and donor-specific immune tolerance, shown by the engraftment of donor skin and second-set islet transplants and acute rejection of a third-party skin. The engraftment of the primary islet allografts with stable chimerism was achieved by the addition of a 2-week peritransplant administration of 15-deoxyspergualin (DSG). Without MSCs, none of the recipients treated with DSG developed chimerism or reversal of diabetes. GVHD was not observed in any of the recipients infused with MSCs (0/15), whereas it occurred in 4/11 recipients without MSCs. These results indicate a potential use of MSCs for induction of hematopoietic chimerism and subsequent immune tolerance in clinical islet transplantation.

Immune properties of mesenchymal stem cells

Mesenchymal stem cells (MSCs) are multipotent progenitor cells isolated by various relatively easily accessible tissues, such as bone marrow and cord blood. MSCs gained attention because of their ease for in vitro expansion together with their multilineage potential. More recently, in vitro and in vivo immunosuppressive properties have been ascribed to them, as they are able to modulate the function of all major immune cell populations, thus impeding immune responses. The underlying mechanisms of their differentiation and function are not thoroughly understood, but still they represent important candidates for tissue regeneration and manipulation of the immune response in graft rejection, graft versus host disease, and autoimmune disorders. Characteristics and immunogenic profile of MSCs, their interface with immune system and their potential use as immunosuppressive elements in cellular therapeutic protocols are reviewed in this chapter.

Screening of genes responsible for differentiation of mouse mesenchymal stromal cells by DNA micro-array analysis of C3H10T1/2 and C3H10T1/2-derived cell lines

BACKGROUND

The molecular mechanisms underlying the biologic effects or differentiation of mesenchymal stromal cells (MSC) have not been clarified. Screening for genes differentially expressed at different stages is an important step in determining these molecular mechanisms.

METHODS

In this study, we analyzed the gene expression profiles of C3H10T1/2 (10T1/2) cells and two sublines, A54 (pre-adipocyte) and M1601 (myoblast), as a model of MSC and downstream committed progenitors.

RESULTS

We found up-regulated expression of delta-like-1 (Dlk), Wnt-5a and IL-1 receptor-like-1 (ST2) in 10T1/2 cells; stem cell factor (SCF) and stromal derived factor-1 (SDF-1) in A54 cells; and cardiac muscle-specific gene in M1601 cells. Overexpression of Dlk in A54 cells did not induce any effects on their differentiation into adipocytes. After differentiation into adipocytes, A54 cells reduced the expression of SCF, SDF-1 and Ang-1 as well as the ability to support the formation of a cobblestone appearance.

DISCUSSION

The results suggest that these three lines hae different gene profiles and are a useful system for analyzing the differentiation and function of MSC and progenitor cells.

The participation of mesenchymal stem cells in tumor stroma formation and their application as targeted-gene delivery vehicles

Recent evidence suggests that mesenchymal stem cells (MSC) selectively proliferate to tumors and contribute to the formation of tumor-associated stroma. The biological rationale for tumor recruitment of MSC remains unclear but may represent an effort of the host to blunt tumor cell growth and improve survival. There is mounting experimental evidence that normal stromal cells can revert malignant cell behavior, and separate studies have demonstrated that stromal cells can enhance tumor progression after acquisition of tumor-like genetic lesions. Together, these observations support the rationale for modifying normal MSC to deliver therapeutic proteins directly into the tumor microenvironment. Modified MSC can produce high concentrations of antitumor proteins directly within the Tumor mass, which have been shown to blunt tumor growth kinetics in experimental animal model systems. In this chapter we will address the biological properties of MSC within the tumor microenvironment and discuss the potential use of MSC and other bone marrow-derived cell populations as delivery vehicles for antitumor proteins.

Mesenchymal stem cells for cardiac regenerative therapy

Until recently, the concept of treating the injured or failing heart by generating new functional myocardium was considered physiologically impossible. Major scientific strides in the past few years have challenged the concept that the heart is a post-mitotic organ, leading to the hypothesis that cardiac regeneration could be therapeutically achieved. Bone marrow-derived adult stem cells were among the first cell populations that were used to test this hypothesis. Animal studies and early clinical experience support the concept that therapeutically delivered mesenchymal stem cells (MSCs) safely improve heart function after an acute myocardial infarction (MI). MSCs produce a variety of cardio-protective signalling molecules, and have the ability to differentiate into both myocyte and vascular lineages. Additionally, MSCs are attractive as a cellular vehicle for gene delivery, cell transplantation or for tissue engineering because they offer several practical advantages. They can be obtained in relatively large numbers through standard clinical procedures, and they are easily expanded in culture. The multi-lineage potential of MSC, in combination with their immunoprivileged status, make MSCs a promising source for cell therapy in cardiac diseases. Here we provide an overview of biological characteristics of MSCs, experimental animal studies and early clinical trials with MSCs. In addition, we discuss the routes of cell delivery, cell tracking experiments and current knowledge of the mechanistic underpinnings of their action.

Adult bone marrow–derived stem cells for organ regeneration and repair

Stem cells have been recognized as a potential tool for the development of innovative therapeutic strategies. There are in general two types of stem cells, embryonic and adult stem cells. While embryonic stem cell therapy has been riddled with problems of allogeneic rejection and ethical concerns, adult stem cells have long been used in the treatment of hematological malignancies. With the recognition of additional, potentially therapeutic characteristics, bone marrow-derived stem cells have become a tool in regenerative medicine. The bone marrow is an ideal source of stem cells because it is easily accessible and harbors two types of stem cells. Hematopoietic stem cells give rise to all blood cell types and have been shown to exhibit plasticity, while multipotent marrow stromal cells are the source of osteocytes, chondrocytes, and fat cells and have been shown to support and generate a large number of different cell types. This review describes the general characteristics of these stem cell populations and their current and potential future applications in regenerative medicine.

Animal serum-free culture conditions for isolation and expansion of multipotent mesenchymal stromal cells from human BM

BACKGROUND

Multipotent mesenchymal stromal cells (MSC) have become important tools in regenerative and transplantation medicine. Rapidly increasing numbers of patients are receiving in vitro-expanded MSC. Culture conditions typically include FSC because human serum does not fully support growth of human MSC in vitro (MSC(FCS)). Concerns regarding BSE, other infectious complications and host immune reactions have fueled investigation of alternative culture supplements.

METHODS

As PDGF has long been identified as a growth factor for MSC, we tested media supplementation with platelet lysate for support of MSC proliferation.

RESULTS

We found that primary cultures of BM-derived MSC can be established with animal serum-free media containing fresh frozen plasma and platelets (MSC(FFPP)). Moreover, MSC(FFPP) showed vigorous proliferation that was superior to classical culture conditions containing FCS. MSC(FFPP) morphology was equivalent to MSC(FCS), and MSC(FFPP) expressed CD73, CD90, CD105, CD106, CD146 and HLA-ABC while being negative for CD34, CD45 and surface HLA-DR, as expected. In addition to being phenotypically identical, MSC(FFPP) could efficiently differentiate into adipocytes and osteoblasts. In terms of immune regulatory properties, MSC(FFPP) were indistinguishable from MSC(FCS). Proliferation of PBMC induced by IL-2 in combination with OKT-3 or by PHA was inhibited in the presence of MSC(FFPP).

DISCUSSION

Taken together, FCS can be replaced safely by FFPP in cultures of MSC for clinical purposes.

Placenta-derived multipotent cells exhibit immunosuppressive properties that are enhanced in the presence of interferon-gamma

Several types of nonhematopoietic stem cells, including bone marrow mesenchymal stem cells (BMMSCs) and embryonic stem cells, have been shown to have immunosuppressive properties. We show that human placenta-derived multipotent cells (PDMCs), which are isolated from a source without ethical concern and harbor multilineage differentiation potential, have strong immunosuppressive properties. PDMCs suppress both mitogen-induced and allogeneic lymphocyte proliferation in both CD4 and CD8 populations. The immunosuppression seen with PDMCs was significantly stronger than that with BMMSCs. Both PDMCs and BMMSCs express indoleamine 2,3-dioxygenase, but only PDMCs are positive for intracellular human leukocyte antigen-G (HLA). Mechanistically, suppression of lymphocyte reactivity by PDMCs is not due to cell death but to decreased cell proliferation and increased numbers of regulatory T cells. Addition of neutralizing antibodies to interleukin-10 and transforming growth factor (TGF)-beta partially restored lymphocyte proliferation. Unlike BMMSCs, PDMCs treated with interferon-gamma for 3 days only very minimally upregulated HLA-DR. On the contrary, PD-L1, a cell surface marker that plays an inhibitory role in T-cell activation, was upregulated and TGF-beta expression was seen. The immunosuppressive properties of PDMCs, along with their multilineage differentiation potential, ease of accessibility, and abundant cell numbers, may render these cells as good potential sources for future therapeutic applications.

Mesenchymal stromal cells

PURPOSE OF REVIEW

Our understanding of the biology and properties of mesenchymal stem cells or multipotent mesenchymal stromal cells has expanded dramatically over the last 3 years and is likely to have an impact on clinical practice in the near future, making a review of this topic both timely and relevant

RECENT FINDINGS

Recommendations regarding nomenclature and the definition of mesenchymal stromal cells have been proposed, a rapidly dividing population within the mesenchymal stromal cell compartment has been better defined and the ability of these cells to exhibit characteristics of cells from a variety of lineages has been extended. The notion that tissue repair with mesenchymal stromal cells is related to transdifferentiation has been re-evaluated and, for the myocardium at least, may be due rather to a paracrine mechanism. The most dramatic developments have been in identifying some of the complex mechanisms underlying the immunosuppressive and nonimmunogenic properties of mesenchymal stromal cells which have important implications for the management of conditions like acute graft-versus-host disease.

SUMMARY

Mesenchymal stromal cells are a biologically important cell population that are able to support hematopoiesis, can differentiate along mesenchymal and nonmesenchymal lineages in vitro, are capable of suppressing alloresponses and appear to be nonimmunogenic. These properties suggest emerging roles for mesenchymal stromal cells in cell therapy.

Immunoregulatory function of mesenchymal stem cells

Mesenchymal stem cells (MSC) are a rare subset of stem cells residing in the bone marrow where they closely interact with hematopoietic stem cells and support their growth and differentiation. MSC can differentiate into multiple mesenchymal and non-mesenchymal lineages, providing a promising tool for tissue repair. In addition, MSC suppress many T cell, B cell and NK cell functions and may affect also dendritic cell activities. Due to their limited immunogenicity, MSC are poorly recognized by HLA-incompatible hosts. Based on these unique properties, MSC are currently under investigation for their possible use to treat immuno-mediated diseases. However, both their condition of immunoprivilege and their immunosuppressive function have recently been challenged when analyzed under particular experimental conditions. Thus, it is likely that MSC effects on the immune system may be deeply influenced not only by cell-to-cell interactions, but also by environmental factors shaping their phenotype and functions.

Multipotent stromal cells from human marrow home to and promote repair of pancreatic islets and renal glomeruli in diabetic NOD/scid mice

We tested the hypothesis that multipotent stromal cells from human bone marrow (hMSCs) can provide a potential therapy for human diabetes mellitus. Severe but nonlethal hyperglycemia was produced in NOD/scid mice with daily low doses of streptozotocin on days 1-4, and hMSCs were delivered via intracardiac infusion on days 10 and 17. The hMSCs lowered blood glucose levels in the diabetic mice on day 32 relative to untreated controls (18.34 mM +/- 1.12 SE vs. 27.78 mM +/- 2.45 SE, P = 0.0019). ELISAs demonstrated that blood levels of mouse insulin were higher in the hMSC-treated as compared with untreated diabetic mice, but human insulin was not detected. PCR assays detected human Alu sequences in DNA in pancreas and kidney on day 17 or 32 but not in other tissues, except heart, into which the cells were infused. In the hMSC-treated diabetic mice, there was an increase in pancreatic islets and beta cells producing mouse insulin. Rare islets contained human cells that colabeled for human insulin or PDX-1. Most of the beta cells in the islets were mouse cells that expressed mouse insulin. In kidneys of hMSC-treated diabetic mice, human cells were found in the glomeruli. There was a decrease in mesangial thickening and a decrease in macrophage infiltration. A few of the human cells appeared to differentiate into glomerular endothelial cells. Therefore, the results raised the possibility that hMSCs may be useful in enhancing insulin secretion and perhaps improving the renal lesions that develop in patients with diabetes mellitus.

Toll-like receptors and their ligands control mesenchymal stem cell functions

Mesenchymal stem cells (MSCs) are widespread in adult organisms and may be involved in tissue maintenance and repair as well as in the regulation of hematopoiesis and immunologic responses. Thus, it is important to discover the factors controlling MSC renewal and differentiation. Here we report that adult MSCs express functional Toll-like receptors (TLRs), confirmed by the responses of MSCs to TLR ligands. Pam3Cys, a prototypic TLR-2 ligand, augmented interleukin-6 secretion by MSC, induced nuclear factor kappa B (NF-kappaB) translocation, reduced MSC basal motility, and increased MSC proliferation. The hallmark of MSC function is the capacity to differentiate into several mesodermal lineages. We show herein that Pam3Cys inhibited MSC differentiation into osteogenic, adipogenic, and chondrogenic cells while sparing their immunosuppressive effect. Our study therefore shows that a TLR ligand can antagonize MSC differentiation triggered by exogenous mediators and consequently maintains the cells in an undifferentiated and proliferating state in vitro. Moreover, MSCs derived from myeloid factor 88 (MyD88)-deficient mice lacked the capacity to differentiate effectively into osteogenic and chondrogenic cells. It appears that TLRs and their ligands can serve as regulators of MSC proliferation and differentiation and might affect the maintenance of MSC multipotency.

Sarcoma derived from cultured mesenchymal stem cells

To study the biodistribution of MSCs, we labeled adult murine C57BL/6 MSCs with firefly luciferase and DsRed2 fluorescent protein using nonviral Sleeping Beauty transposons and coinfused labeled MSCs with bone marrow into irradiated allogeneic recipients. Using in vivo whole-body imaging, luciferase signals were shown to be increased between weeks 3 and 12. Unexpectedly, some mice with the highest luciferase signals died and all surviving mice developed foci of sarcoma in their lungs. Two mice also developed sarcomas in their extremities. Common cytogenetic abnormalities were identified in tumor cells isolated from different animals. Original MSC cultures not labeled with transposons, as well as independently isolated cultured MSCs, were found to be cytogenetically abnormal. Moreover, primary MSCs derived from the bone marrow of both BALB/c and C57BL/6 mice showed cytogenetic aberrations after several passages in vitro, showing that transformation was not a strain-specific nor rare event. Clonal evolution was observed in vivo, suggesting that the critical transformation event(s) occurred before infusion. Mapping of the transposition insertion sites did not identify an obvious transposon-related genetic abnormality, and p53 was not overexpressed. Infusion of MSC-derived sarcoma cells resulted in malignant lesions in secondary recipients. This new sarcoma cell line, S1, is unique in having a cytogenetic profile similar to human sarcoma and contains bioluminescent and fluorescent genes, making it useful for investigations of cellular biodistribution and tumor response to therapy in vivo. More importantly, our study indicates that sarcoma can evolve from MSC cultures.

Enhanced Engraftment of Mesenchymal Stem Cells in a Cutaneous Wound Model by Culture in Allogenic Species-Specific Serum and Administration in Fibrin Constructs

Human mesenchymal stem cells (hMSCs), also referred to as multipotent stromal cells, are currently being applied in clinical trials for bone diseases, graft versus host disease, and myocardial infarction. However, the standard growth medium for hMSCs contains 10%-20% fetal calf serum (FCS), and FCS is strongly immunogenic in both rodents and humans. Previously, we reported that by a sensitive fluorescence-based assay, 7-30 mg of internalized FCS is associated with 10(8) hMSCs, a dosage that will probably be needed for most therapies. We also found that a brief culture in medium containing autologous 20% adult human serum (AHS) or autologous 10% AHS supplemented with growth factors (AHS(+)) reduced the contamination by more than 99.9%. We have now extensively characterized the culture conditions and shown that hMSC expansion is possible using heterologous 20% AHS or heterologous 10% AHS(+). The uptake of FCS is an active process that acts to concentrate contamination in the cells even under low serum conditions (2% FCS) but can be actively displaced by incubation of the cells in medium with AHS. Rat MSCs (rMSCs) can be expanded under similar conditions using supplemented heterologous adult rat serum (ARS(+)). After expansion in FCS, a further 8 days of culture with ARS(+) significantly improves the viability of the rMSCs in vivo after encapsulation in fibrin followed by subcutaneous implantation in rats. Our results have the potential to dramatically improve cellular and genetic therapies using hMSCs.